Techniques interesting to the present invention are described in, for example, Japanese Patent Laid-open Publication No. 10-279903 (Patent Document 1) and International Publication No. WO 2004/053901 (Patent Document 2).
Patent Document 1 describes, in claim 1 thereof, a conductive adhesive including: particles (A) formed of a low-melting-point metal with a melting point of 300° C. or lower; conductive particles (B) having a melting point higher than the melting point of the low-melting-point metal; and an organic binder, wherein the total amount of A and B is 70 to 95% by weight, and the blending ratio of A:B is 5:95 to 50:50 (weight ratio).
In regard to the blending ratio of the low-melting-point metal (A) in the conductive adhesive, it is provided in claim 1 of Patent Document 1 that the blending ratio of the low-melting-point metal (A) is 5 to 50% by weight. However, as a result of experiments conducted by the present inventors, it has become apparent that when the conductive adhesive described in Patent Document 1 is used for forming an external electrode in a laminated ceramic electronic component that includes an internal electrode containing Ni, the external electrode has poor bondability to the internal electrode if the blending ratio of the low-melting-point metal (A) is less than 36.5% by weight, or more than 47.8% by weight.
On the other hand, Patent Document 2 describes, in claim 1 thereof, a laminated ceramic electronic component including an external electrode formed of a thermosetting conductive paste that contains a metal powder (metal A) having a melting point of 300° C. or lower, high-melting-point conductive particles (metal B), and a resin. It is provided in claim 2 of Patent Document 2 that the total amount of A and B in the paste is 70 to 95% by weight based on the total amount of A, B and the resin. It is provided in claim 3 of Patent Document 2 that the blending ratio of A:B is 5:95 to 20:80 in terms of a weight ratio. It is provided in claim 4 of Patent Document 2 that the paste is held at 80 to 400° C. for 1 to 60 minutes for obtaining an external electrode. It is provided in claim 5 of Patent Document 2 that the conductive particles in the external electrode and the metal of the internal electrode are diffusion-bonded to each other.
In regard to the blending ratio of the low-melting-point metal (A), it is provided in claim 3 of Patent Document 2 that the blending ratio of the low-melting-point metal (A) is 5 to 20% by weight. However, as a result of experiments conducted by the present inventors, it has become apparent that when the conductive adhesive described in Patent Document 2 is used for forming an external electrode in a laminated ceramic electronic component that includes an internal electrode containing Ni, the external electrode has poor bondability to the internal electrode because the ratio of the low-melting-point metal (A) is as low as 5 to 20% by weight. If a heat treatment is performed at a temperature above the range of 80 to 400° C. as specified in claim 4, for example 500° C. or higher, the external electrode can be satisfactorily bonded to the internal electrode, but metal balls are deposited (or erupted) from the external electrode, and therefore a plating failure occurs in a plating step such as Ni plating which is subsequently carried out.
Patent Document 1: Japanese Patent Laid-open Publication No. 10-279903
Patent Document 2: International Publication No. WO 2004/053901